Electrochemical sensors with a sensor chip are used in laboratories and also in production plants to detect different chemical and/or physical parameters. An example is a pH sensor with an ion-sensitive field effect transistor (ISFET) as sensor chip.
Use in production plants and under process conditions, in particular, requires the sensor to be extremely robust. A sensor chip such as an ISFET, for example, should, however, be in direct contact with the medium to be measured in order to take a measurement, which makes it necessary for the sensor to exhibit at least one opening. The sensor chip is arranged in the sensor in such a manner that at least the sensitive region thereof can be brought into contact with the measuring medium through this opening. Process-approved sensors frequently exhibit a substantially cylindrical sensor body with standard dimensions, so that these can easily be integrated into existing process plants.
A challenge is posed by the use of electrochemical sensors of this kind in biological, biotechnological, food-chemical and/or pharmaceutical process plants and also in laboratories in these sectors. Uses in these sectors require the sensor to be hygienic and satisfy the corresponding standards. A hygienic sensor is characterized in that wherever possible no substances are deposited on the sensor and/or are able to multiply there, as this kind of contamination causes biofouling, for example, and/or it can even contaminate an entire process.
It is therefore important in an application of this kind to ensure optimal encapsulation of the sensor chip in the sensor, which on the one hand allows direct contact between the sensitive region and the measuring medium and, on the other hand, at least guarantees a fluid-tight seal between the measuring medium and the inside of the sensor, so that no measuring medium is able to penetrate the sensor.
The possible ways of encapsulating sensor chips are described for example in W. Oelpner et al. “Encapsulation of ISFET Sensor Chips”, Sensors and Actuators B 105 (2005) 104-117 and V. L. Khanna “Critical issues, processes and solutions in ISFET packaging”, Microelectronics Int. 25/2 (2008) 23-30 and range from the simple adhesion of the sensor chip, through the use of an attachment with a sensor chip mounted between two seals (EP 1 396 718 A1) or the pouring of a hardenable filling substance into the inside of the sensor to pressing in with a stopper which presses the sensor chip against a seal enclosing the opening.
Known annular gasket s or also a laser-cut seal adapted to the sensor type can be used as seal, as for example disclosed in DE 10 2009 026 991 A1.
The disadvantage of the known sensors is that they frequently fail to meet the requirements made in fields such as for example biochemistry, biotechnology, food chemistry and/or pharmaceuticals, in relation to a hygienically configured sensor, as the sensor exhibits production-related cracks, gaps or undercuts in the region that comes into contact with the measuring medium and these allow the settlement and accumulation of substances from the measuring medium, as a result of which the service life of the sensor can be shortened due to the penetrating measuring medium and/or measuring errors can result, for example. The formation of gaps or cracks may be caused by the insertion of sealing elements in the sensor body, for example. These sealing elements are used to close off access to the sensor body, through which the sensor chip is introduced into the sensor body.
The object of the invention is therefore the development of an electrochemical sensor with a sensor chip which is in particular of hygienic design. In addition, the sensor should be easy to fit, in other words easily assembled.